Bearings, which are configured to be mounted to a wheel of an automotive vehicle, may be classified into a bearing using balls as rolling elements and a bearing using tapered rollers as rolling elements according to the type of rolling elements.
FIG. 1 is a sectional view of a prior art hub bearing unit 100, which uses balls as rolling elements. The hub bearing unit 100 shown in FIG. 1 includes: a hub 110 formed with an inner race surface 113 and having a flange 111, to which a wheel (not shown) is mounted; an inner ring 120 formed with an inner race surface 121 and being mounted to one side of an outer peripheral surface 115 of the hub 110; an outer ring 130 formed with double-row outer race surfaces 131 and having a flange 133, to which a knuckle (not shown) is mounted; balls 140 (rolling elements) disposed in double rows between the inner race surfaces 113 and 121 and the outer race surface 131; a cage 150 formed with a plurality of grooves receiving the balls 140 therein for maintaining the balls 140 at constant circumferential intervals; and seals 160 fitted between the hub 110 and the outer ring 130 and between the inner ring 120 and the outer ring 130 to prevent foreign substances from entering inward and also to prevent lubricant filled inside from leaking. In FIG. 1, a reference numeral 103 denotes a bolt for securing a wheel to the hub 110. A reference numeral 111a denotes a hole, to which the bolt 103 is inserted and fixed. A reference numeral 133a denotes a hole, at which a knuckle (not shown) is joined and fixed to the flange 133.
FIG. 2 is a sectional view of a prior art hub bearing unit 200, which uses tapered rollers as rolling elements. The hub bearing unit 200 shown in FIG. 2 includes: a hub 210 formed with an inner race surface 213 and having a flange 211, to which a wheel (not shown) is mounted; an inner ring 220 formed with an inner race surface 221 and being mounted to one side of an outer peripheral surface 215 of the hub 210; an outer ring 230 formed with double-row outer race surfaces 231 and having a flange 233, to which a knuckle (not shown) is mounted; tapered rollers 240 (rolling elements) disposed in double rows between the inner race surfaces 213 and 221 and the outer race surface 231; a retainer 250 formed with a plurality of through-holes receiving the rollers 240 therein for maintaining the rollers 240 at constant circumferential intervals; and seals 260 fitted between the hub 210 and the outer ring 230 and between the inner ring 220 and the outer ring 230 to prevent foreign substances from entering inward and also to prevent lubricant filled inside from leaking. In FIG. 2, a reference numeral 203 denotes a bolt for securing a wheel to the hub 210. A reference numeral 211a denotes a hole, to which the bolt 203 is inserted and fixed. A reference numeral 233a denotes a hole, at which a knuckle (not shown) is joined and fixed to the flange 233.
When an automotive vehicle with the hub bearing unit 100, 200 mounted to its wheel travels, an axial load indicated by Fa and a longitudinal load indicated by Fr act on the hub bearing unit 100, 200, respectively. The axial load Fa is produced when the automotive vehicle turns left or right.
The hub bearing unit 100, the rolling elements of which are balls, is advantageous in that its rolling resistance is low when it works as mounted to the automotive vehicle. However, there is a problem since it can be mounted to only passenger cars or small SUVs as it has low load capability against external loads. On the contrary, the hub bearing unit 200, the rolling elements of which are tapered rollers, is advantageous in that it can support heavier loads and its life is long. However, there is a problem in that its rolling resistance and manufacturing costs are high compared to the hub bearing unit 100, which uses balls as rolling elements.